Emergence of a novel PRRSV-1 strain in mainland China: a
recombinant strain derived from the two commercial modified live viruses
Amervac and DV
Qi Suna1, Hu Xu a1, Chao Lia, Bangjun Gonga, Zhen
Lib, Zhi-Jun
Tiana, Hongliang
Zhanga*
a State Key
Laboratory of Veterinary Biotechnology, Harbin Veterinary Research
Institute, Chinese Academy of Agricultural Sciences, Harbin 150001,
China
b Pingdingshan Center For Animal Disease Control And
Prevention, Pingdingshan 467000, China
1 These authors contributed equally to this work.
* Corresponding author contact information: Harbin Veterinary Research
Institute, CAAS, No. 678 Haping Road, Xiangfang District, Harbin 150001,
China.
Tel.: +86-13624503578
E-mail address: zhanghongliang01@caas.cn
Abstract: Porcine
reproductive and respiratory syndrome virus 1 (PRRSV-1) is one of the
main pathogens causing porcine reproductive and respiratory syndrome
(PRRS). In recent years, the
detection number of PRRSV-1 in China has gradually increased, and the
PRRSV-1 strains reported in China belong to subtype Ⅰ (Global; Clade
A-L). In the present study, a
novel PRRSV-1 strain, TZJ2134, was found during epidemiological
surveillance of PRRSV-1 in Shandong Province in China. We obtained two
fragments of TZJ2134: TZJ2134-L12 (located at nt 1672-nt 2112 in the
partial Nsp2 gene) and TZJ2134-(A+B) (located at nt 7463-nt 11272 in the
partial Nsp9, complete Nsp10 and partial Nsp11 genes).
Phylogenetic and recombination
analyses based on the two sequences showed that TZJ2134 is a recombinant
strain derived from two commercial
PRRSV-1 modified live vaccine (MLV) strains (the Amervac vaccine and DV
vaccine strains), forming a new recombinant subgroup of DV+Amervac-like
isolates with other strains. However, PRRSV-1 MLV is not currently
allowed for use in China. We
speculated that TZJ2134 might have been introduced from Europe. This
study is the first to provide information on two recombinant PRRSV-1 MLV
strains in China and provides new data for the epidemiological study of
PRRSV-1 in China.
KEYWORDS: PRRSV-1, Vaccine, Recombination, Novel strains.
1 INTRODUCTION
Porcine reproductive and respiratory
syndrome (PRRS) is a highly contagious disease causing substantial
economic losses in the swine industry worldwide. It is mainly
characterized by widespread reproductive failure in pregnant sows and
respiratory symptoms in pigs of all ages (Butler et al., 2014). PRRSV is
divided into two species, namely, Betaarterivirus suid 1 (PRRSV-1) and
Betaarterivirus suid 2 (PRRSV-2) (Walker et al., 2020), which share only
50–60% nucleotide sequence identity (Murtaugh, Faaberg, Laber, Elam,
& Kapur, 1998) and have attracted increasing attention due to the high
incidence of PRRSV mutation and recombination. Based on the phylogenetic
analysis of ORF5 nucleotide sequences and the global PRRSV
classification system, PRRSV-1 is divided into 4 subtypes: subtype Ⅰ
(Global; Clade A-L), subtype Ⅰ (Russian), subtype Ⅱ, and subtype Ⅲ.
PRRSV-2 can be divided into 9 subtypes: lineages 1~9
(Shi et al., 2010).
PRRSV-1 and PRRSV-2 have significant
differences in geographical distribution. PRRSV-2 was isolated in 1992
in America (ATCC-VR2332, the North American prototypic strain)
(Wensvoort et al., 1992) and is mainly prevalent in North America and
Asia(Brar, Shi, Murtaugh, & Leung, 2015). PRRSV-1 was isolated in 1991
in the Netherlands (Lelystad virus, the European prototypic strain)
(Collins et al., 1992) and is mainly prevalent in Europe. However, only
subtype Ⅰ (Global; Clade A-L) has spread to continents other than
Europe. The remaining subtypes have been reported only in Eastern
European countries and Russia (Stadejek, Stankevicius, Murtaugh, &
Oleksiewicz, 2013). In 2011, Chen et al. isolated PRRSV-1 strains
(BJEU06-1, NMEU09-1) in China, which was the first report of wild
PRRSV-1 isolates in mainland China (Chen et al., 2011). To date, PRRSV-1
has been prevalent in at least 20 provinces in China (Chen et al., 2020;
Gao et al., 2017; Liu et al., 2017; X. Wang et al., 2016; Q. Zhang et
al., 2020; Zhou et al., 2015). In recent years, the detection number of
PRRSV-1 in China has gradually increased. The PRRSV-1 strains reported
in China all belong to subtype Ⅰ (Global) and can be divided into four
subgroups (NMEU09-1-like, Amervac-like, HKEU16-like, and BJEU06-1-like
isolates) (Chen et al., 2017). However, compared with the large number
of PRRSV-2 infections in China, the number of PRRSV-1 infections
detected was relatively low (Lin et al., 2020; Zhai et al., 2018). We
speculated that the reason might be that PRRSV-1 is not given much
attention because it is not the main epidemic strain in China, and there
is evidence that most PRRSV-1-infected pigs in China exhibit mild
clinical symptoms (Ming et al., 2017; X. Wang et al., 2016). Even so,
the effect of PRRSV-1 on pigs should not be ignored.
Vaccination is a key strategy for PRRSV-1 prevention and control.
In the late 1990s, PRRSV-1 MLV was
used in Europe(Chae, 2021). Nevertheless, the particularly high
variability of PRRSV and the possibility of vaccine revertant PRRSV
emerging in pigs vaccinated with PRRSV MLV could result in recombination
between different MLV strains (Eclercy et al., 2019; Kvisgaard et al.,
2020) or recombination between MLV strains and wild-type PRRSV strains
(Chen et al., 2017; Marton et al., 2019; Wang et al., 2019). This
indicates the importance of the rational use of vaccines. In this study,
a novel PRRSV-1 strain was identified in the epidemiological
investigation of PRRSV in China; this strain was derived from
recombination of two commercial PRRSV-1 MLV strains (Amervac vaccine
strain and DV vaccine strain).